Performance of hydrophilic polyols in the formation of polyurethane based controlled release fertilizer coatings

Abstract

A series of controlled-release coatings were developed for granular urea (46-0-0) using a layer-by-layer polyurethane system composed of polyether polyol blends, polymeric methylene diphenyldiisocyanate (pMDI), and a wax additive. A coating formulation utilizing a hydrophobic poly(propylene oxide) triol (P700) served as a baseline for release performance. Surprisingly, hydrophilic poly(ethylene oxide)-based diols and triols, when blended with approximately 20% glycerol, yielded coatings with improved crosslink density and moderated curing kinetics. Notably, glycerol inclusion did not enhance P700 performance, but its combination with poly(ethylene oxide)-based diol resulted in a synergistic improvement in release control for the coating formulations. These hydrophilic blended systems not only achieved excellent controlled-release behavior but also outperformed the hydrophobic P700-based coatings. This study demonstrates that hydrophilic polyols, when properly formulated, can rival or exceed the performance of traditional hydrophobic systems, offering new design strategies for environmentally responsive and tunable nutrient release coatings.